Working with TOML

Elm:
Working with TOML

How to:

Elm doesn’t have a built-in TOML parser, but you can interop with JavaScript or use a community package. Here’s how you might parse TOML using a hypothetical elm-toml package:

import Toml

configToml : String
configToml =
    """
    [server]
    port = 8080
    """

parseResult : Result Toml.Decode.Error Toml.Value
parseResult =
    Toml.decodeString configToml

For decoding specific values:

portDecoder : Toml.Decode.Decoder Int
portDecoder =
    Toml.Decode.field "server" (Toml.Decode.field "port" Toml.Decode.int)

port : Result String Int
port =
    Toml.decodeString portDecoder configToml

Sample output for port might be Ok 8080 if the decoding succeeds.

Deep Dive

TOML was created by Tom Preston-Werner, co-founder of GitHub, as a simple language for configuration files. It competes with YAML and JSON; TOML’s syntax aims for the best of both worlds with a focus on being easy for humans to read and write.

In Elm, to handle TOML, you typically need to go through JavaScript interop, which can be a bit of a hassle. Thankfully, the Elm community is resourceful, and several third-party packages exist. The hypothetical elm-toml package would likely use Elm’s Port to talk to a JavaScript TOML parser or implement the parsing directly in Elm.

The main hurdle in Elm is that it statically types everything, so you’ll need to write custom decoders to handle different data structures within TOML, which can be a bit verbose but adds safety.

Elm:Working with TOML

How to:

Deep Dive

See Also

Elm:
Working with TOML